- For i386 this is currently highly experimental and should be only+ For 32-bit this is currently highly experimental and should be only used for kernel development. It might also cause boot failures.- For x86_64 this is recommended on all multiprocessor Opteron systems.+ For 64-bit this is recommended on all multiprocessor Opteron systems. If the system is EM64T, you should say N unless your system is EM64T NUMA.